Abstract: Seasonal patterns and annual variations of ozone in the planetary boundary layer are analyzed using observational data recorded over the western Pacific during 2000-2010. The datasets include ozone sounding data at Hong Kong, Sapporo, and Naha; satellite retrieval tropospheric excess columns of NO₂; surface ozone; and meteorological variables. The results show patterns of ozone that differ significantly at the three sites. Both Hong Kong and Naha show bimodal patterns with peak values in spring and autumn and the lowest value in summer, whereas Sapporo shows one peak in spring. Meteorological conditions and human activities account for such differences in seasonal patterns. Similar increase rates of ozone (0.80 versus 0.77 ppb a^-1) (ppb represents 10^-9) are detected within the planetary boundary layer at both Naha and Sapporo sites. Hong Kong shows the smallest annual change but the largest increase rate (1.21 ppb a^-1) in autumn. The tropospheric columns of NO₂ retrieved from GOME (Global Ozone Monitoring Experiment) and SCIAMACHY (Scanning Imaging Absorption Spectro Meter for Atmospheric Chartography) measurements indicate that the increasing ozone within the planetary boundary layer at Sapporo, Naha (annual mean), and Hong Kong (seasonal mean in autumn) result from increasing anthropogenic emissions and regional transport. The cluster analyses of backward trajectories calculated with HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model further confirm that the increases in ozone over Naha and Sapporo are attributed to the regional transport from northeastern China.